Small weight university abandoned in the past (4)
I believe the answer is:
once
'in the past' is the definition.
(once upon a time)
'small weight university abandoned' is the wordplay.
'small weight' becomes 'ounce' (I've seen this before).
'university' becomes 'U' (abbreviation as in UMass).
'abandoned' is a deletion indicator.
'ounce' with 'u' taken away is 'ONCE'.
(Other definitions for once that I've seen before include "in bygone era" , "On a single (or past) occasion" , "In days gone by" , "Formerly, at one time" , "At some time past" .)